Modelling a surfactant-covered droplet on a solid surface in three-dimensional shear flow

Liu, Haihu1; Zhang, Jinggang1; Ba, Yan2; Wang, Ningning1; Wu, Lei3

2020-08-25

10.1017/jfm.2020.416

JOURNAL OF FLUID MECHANICS   影响因子和分区

0022-1120

1469-7645

A surfactant-covered droplet on a solid surface subject to a three-dimensional shear flow is studied using a lattice-Boltzmann and finite-difference hybrid method, which allows for the surfactant concentration beyond the critical micelle concentration. We first focus on low values of the effective capillary number (Ca-e) and study the effect of Ca-e, viscosity ratio (lambda) and surfactant coverage on the droplet behaviour. Results show that at low Ca-e the droplet eventually reaches steady deformation and a constant moving velocity u(d). The presence of surfactants not only increases droplet deformation but also promotes droplet motion. For each lambda, a linear relationship is found between contact-line capillary number and Ca-e, but not between wall stress and u(d) due to Marangoni effects. As lambda increases, u(d) decreases monotonically, but the deformation first increases and then decreases for each Ca-e. Moreover, increasing surfactant coverage enhances droplet deformation and motion, although the surfactant distribution becomes less non-uniform. We then increase Ca-e and study droplet breakup for varying lambda, where the role of surfactants on the critical Ca-e (Ca-e,Ca-c) of droplet breakup is identified by comparing with the clean case. As in the clean case, Ca-e,Ca-c first decreases and then increases with increasing lambda, but its minima occurs at lambda = 0.5 instead of lambda = 1 in the clean case. The presence of surfactants always decreases Ca-e,Ca-c, and its effect is more pronounced at low lambda. Moreover, a decreasing viscosity ratio is found to favour ternary breakup in both clean and surfactant-covered cases, and tip streaming is observed at the lowest lambda in the surfactant-covered case.

contact lines breakup coalescence Marangoni convection

SCI ; EI

英语

其他

National Natural Science Foundation of China[51876170] ; Natural Science Basic Research Plan in Shaanxi Province of China[2019JM-343] ; National Key Research and Development Project of China[2016YFB0200902]

Mechanics ; Physics

Mechanics ; Physics, Fluids & Plasmas

WOS:000542764100001

CAMBRIDGE UNIV PRESS

20202708902082

Capillarity ; Viscosity ; Micelles ; Critical micelle concentration ; Deformation ; Drop breakup

Fluid Flow, General:631.1 ; Colloid Chemistry:801.3 ; Physical Properties of Gases, Liquids and Solids:931.2

ENGINEERING

Web of Science

1.Xi An Jiao Tong Univ, Sch Energy & Power Engn, 28 West Xianning Rd, Xian 710049, Peoples R China
2.Northwestern Polytech Univ, Sch Astronaut, 127 West Youyi Rd, Xian 710072, Peoples R China
3.Southern Univ Sci & Technol, Dept Mech & Aerosp Engn, Shenzhen 518055, Peoples R China

Liu, Haihu,Zhang, Jinggang,Ba, Yan,et al. Modelling a surfactant-covered droplet on a solid surface in three-dimensional shear flow[J]. JOURNAL OF FLUID MECHANICS,2020,897.

Liu, Haihu,Zhang, Jinggang,Ba, Yan,Wang, Ningning,&Wu, Lei.(2020).Modelling a surfactant-covered droplet on a solid surface in three-dimensional shear flow.JOURNAL OF FLUID MECHANICS,897.

Liu, Haihu,et al."Modelling a surfactant-covered droplet on a solid surface in three-dimensional shear flow".JOURNAL OF FLUID MECHANICS 897(2020).